1. Detailed Description of the Invention
The present invention relates to a circularly polarized wave antenna for use in communication between a stationary satellite and a movable body.
2. Description of the Prior Art
Since in a system for communicating with the stationary satellite or receiving satellite broadcasting in a movable body such as an automobile, a circularly polarized wave is mainly used, there is desired a small-sized circularly polarized wave antenna through which an excellent circularly polarized wave can be obtained within a wide range of angle of elevation.
FIG. 6 shows a conventional example of this sort of circularly polarized wave antenna, and FIG. 6A is a perspective view showing a circularly polarized wave antenna; and FIG. 6B is a side view showing the circularly polarized wave antenna. This circularly polarized wave antenna 101 is composed of a ground plate 102 and four conductors 103. These conductors 103 are obtained by extending a central conductor of a coaxial cable 104. Also, an outer conductor of the coaxial cable 104 is soldered to the ground plate 102 at a soldered point 105 as shown. Accordingly, each conductor 103 is fixed onto the ground plate 102 like a cantilever. Also, each conductor 103 is arranged on the ground plate 102 at regular intervals d, and inclines at a predetermined angle xcex1 in the same direction respectively.
In the circularly polarized wave antenna 101 constituted as described above, electric power is fed to those four conductors 103 in phase to create a phase difference of 90xc2x0 in space, whereby the main beam faces a certain angle of elevation, a circularly polarized wave can be emitted in that direction, and further a pattern of a conical surface at the angle of elevation becomes non-directional. In other words, the directivity of the circularly polarized wave antenna 101 becomes as shown in FIG. 7 even if viewed from any of the azimuth angle directions, and if the stationary satellite 107 is positioned on an extension line of an oblique line 106, the directivity of the circularly polarized wave antenna 101 can always be directed toward the stationary satellite 107 in whichever direction the movable body equipped with the circularly polarized wave antenna 101 may advance. In this case, when the target angle of elevation is within, for example, a range of 30xc2x0 to 60xc2x0, if an angle of inclination a of the conductor 103 is set to about 45xc2x0, the length L of the conductor 103 is set to about 0.65 xcex0, an interval d between two conductors 103 in opposite to each other is set to about 0.33 xcex0, then the optimum directivity to the angle of elevation can be obtained (where xcex0 is free space wave length of the radio wave for use)
Since the above-described conventional circularly polarized wave antenna 101 has been constructed such that four conductors 103 which have been inclined by about 45xc2x0 are arranged on the ground plate 102 at a regular interval d so as to feed electric power to each conductor 103 in phase, there is no need for any automatic phase shifter and the like on feeding electric power and there is an advantage that the structure can be simplified. However, the structure is not without its problems. More specifically, since four conductors 103 (about 0.65 xcex0 in length) inclined by about 45xc2x0 are arranged at a regular interval d (about 0.33 xcex0), the overall dimension of the circularly polarized wave antenna 101 becomes 0.33 xcex0xc3x970.33 xcex0xc3x970.46 xcex0, when the frequency for use is, for example, 2.3 GHz (xcex0=130 mm), becomes as large as up to about 43xc3x9743xc3x9760 (mm), and miniaturization as a vehicle-mounted antenna cannot be realized. Also, since each conductor 103 is only fixed onto the ground plate 102 in a cantilever shape and has low mechanical strength, there is a problem that the interval between each conductor 103 fluctuates because of vibration of the automobile to deteriorate the antenna characteristics or great stress is applied to a soldered point 105 of an outer conductor of the coaxial cable 104 to cause a poor connection.
The present invention has been achieved in views of the prior art as such, and is aimed to provide a circularly polarized wave antenna at low prices which is suitable for miniaturization and is also resistant to vibrations.
As solution means for achieving the above-described object, there is provided a circularly polarized wave antenna, according to the present invention, having four flat plate-shaped dielectrics having the substantially same thickness vertically provided on a printed substrate and arranged in a square-cylinder shape as a whole, and four radiation conductors provided on each outer wall surface of these flat plate-shaped dielectrics inclined in a fixed direction, characterized in that the structure is arranged such that a lower end of each of the above-described radiation conductors is electrically connected to the printed substrate and such that electric power is fed to these four radiation conductors in phase.
In a circularly polarized wave antenna constructed as described above, since there are provided radiation conductors on each outer wall surface of four flat plate-shaped dielectrics arranged in a square cylinder shape, a mechanical orthogonal relationship of each radiation conductor is retained so that not only deterioration in the antenna characteristics and the poor connection resulting from external vibrations can be reduced but also the required length of the radiation conductor becomes short by a shortened wavelength due to the flat plate-shaped dielectric having high specific inductive capacity, and as a result, substantial miniaturization can be realized. Also, since the flat plate-shaped dielectric is not likely to unevenly contract in a calcination process during manufacture, it is also easy to perform fine adjustment of the plate thickness and the like by polishing after the calcination, it becomes easy to prevent variations in the antenna characteristics resulting from dimensional error or the like. Further, since it is easy to print the radiation conductor on a flat surface which serves as the outer wall surface of the flat plate-shaped dielectric, not only is it possible to easily form a desired radiation conductor by raising the printing precision but also it is possible to collectively print and form the radiation conductor on a multiplicity of flat plate-shaped dielectrics having the substantially same thickness. Therefore, the printing cost can be significantly reduced.
Also, if, in the above-described structure, of a pair of flat plate-shaped dielectrics adjacent substantially at right angles, a protrusion for protruding from the side of one flat plate-shaped dielectric by a portion corresponding to the plate thickness is fitted into a recess obtained by cutting a portion corresponding to the plate thickness in the side of the other flat plate-shaped dielectric, it will be possible to combine four flat plate-shaped dielectrics having the same width dimension in a square-cylinder shape at a layout of a substantial square. Therefore, it becomes easier to design and perform an assembly operation.
Further, if, in the above-described structure, those four flat plate-shaped dielectrics are all of the same shape, the manufacturing cost can also be significantly reduced. In this case, if an upper half of one side and a lower half of the other side of the flat plate-shaped dielectric are cut by a portion corresponding to the plate thickness along the direction of the width, it is possible to adopt a structure preferable in design in which a protrusion of one flat plate-shaped dielectric adjacent substantially at right angles is fitted into a recess in the other flat plate-shaped dielectric whereby four flat plate-shaped dielectrics are combined in a square-cylinder shape in a layout of a square as well as it is possible to remarkably enhance the dimensional precision because the protrusion concerned and the recess concerned have the same contraction condition in the calcination process.